1. Field of the Invention
The present invention relates to a multi-piece solid golf ball comprising an elastic solid core, a resinous cover enclosing the core and a resinous intermediate layer therebetween having different physical properties, which ball provides excellent spin and flight performances.
2. Background Art
Multi-piece solid golf balls having an elastic solid core and a cover composed of at least two layers have already been proposed as golf balls which meet the requirements of professionals and other skilled golfers. For example, JP-A 7-24085 discloses a golf ball with an inside hard/outside soft cover construction in which the inner cover layer has a greater hardness than the outer cover. JP-A 10-15 1226 discloses a multi-piece solid golf ball of the same type which has an improved spin performance, durability and flight distance.
However, such improvements remain inadequate. A need continues to be felt for golf balls having certain qualities desired in particular by professionals and other skilled golfers, such as better spin performance when hit with an iron or on approach shots and better flight performance.
It is therefore an object of the invention to provide a multi-piece solid golf ball in which the deformations of ball components under increasing load conditions simulating the deformation of the ball on actual shots are optimized so as to improve flight performance and spin performance when hit with an iron and on approach shots.
This invention is directed to a multi-piece solid golf ball comprising an elastic solid core, a resinous cover enclosing the core and formed with a plurality of dimples, and a resinous intermediate layer between the core and the cover. The elastic solid core, a sphere consisting of the solid core and the intermediate layer enclosing the core, and the golf ball (as a completed article having the solid core enclosed with the intermediate layer and the cover) each undergo a deformation when the load applied thereto is increased from an initial load of 98 N (10 kgf) to a final load of 1274 N (130 kgf). Provided that A, B and C represent the deformations that the solid core, the sphere consisting of the solid core and the intermediate layer enclosing the core, and the golf ball undergo, respectively, the deformations of the respective components are adjusted so as to satisfy the relationship: 1.14xe2x89xa6A/Bxe2x89xa61.30 and 1.05xe2x89xa6B/Cxe2x89xa61.16. Then the deformations of the ball components under increasing load conditions simulating the deformation of the ball upon actual shots are mutually optimized, and the deformation of the golf ball is properly balanced throughout the ball. Due to synergistic effects of the optimization combined with the good balance, the multi-piece solid golf ball has excellent flight performance and improved spin performance when hit with an iron and on approach shots.
Accordingly, the invention provides a multi-piece solid golf ball comprising an elastic solid core, a resinous cover enclosing the core and formed with a plurality of dimples, and a resinous intermediate layer between the core and the cover. When subjected to a load of 1274 N (130 kgf) from an initial load of 98 N (10 kgf), the solid core undergoes a deformation A, a sphere consisting of the solid core and the intermediate layer enclosing the core undergoes a deformation B, and the golf ball undergoes a deformation C, all expressed in millimeter, which satisfy the relationship:
xe2x80x831.14xe2x89xa6A/Bxe2x89xa61.30
and
1.05xe2x89xa6B/Cxe2x89xa61.16.
In a preferred embodiment, the cover is composed primarily of a thermoplastic or thermosetting polyurethane elastomer. The intermediate layer is preferably made of a resin composition comprising at least 70 parts by weight of ionomer resin, more preferably a resin composition comprising:
(a) 100 parts by weight of an olefin/unsaturated carboxylic acid random copolymer, an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random copolymer, a metal ion neutralization product of either type of copolymer, or a mixture of any of the copolymers and the neutralization products thereof;
(b) 5 to 80 parts by weight of a fatty acid having a molecular weight of at least 280 or a derivative thereof; and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing the acid groups in components (a) and (b).
Preferably, the dimples have a V0 value of up to 0.47. V0 is the volume of a dimple space below a plane circumscribed by the dimple edge divided by the volume of a cylinder whose bottom is the plane and whose height is the maximum depth of the dimple from the bottom.